1. Field of the Invention
This invention relates to a method of removing residual liquid hydrocarbons such as oil from pipe systems. More particularly, this invention relates to the flushing of residual amounts of oil, sediment and other impurities from pipe systems, particularly ballast discharge lines on board ships in which sea water is the principal fluid for flushing and/or after draining of such pipe systems.
2. Prior Art
Crude oil tankers normally use the same pumps and piping lines to handle both cargo and clean ballast water; therefore, tankers must effectively flush the crude oil from these lines during the ballast voyage in order to avoid contaminating water at the crude loading port environment during clean ballast water discharge at the port. This water flushing operation is very difficult and time-consuming because of the complexity of the piping network and the large number of deadended branches in the pipe system. Also, only very limited direct water flushings of discharge lines from cargo and clean ballast tanks occurs during crude oil tank cleaning operations. Typically, 2 to 4 hours of water flushing per day for several days must be dedicated to this cleaning operation to get the tanker pipe system sufficiently clean so that substantially no crude oil or other associated impurities will be released from the pipe system and discharged in port with the clean ballast water; and, despite such extensive cleaning operations, experience has shown that a gradual release of oil film can occur from dead-end piping sections and valves which can recontaminate the lines and subsequently the discharged ballast water. Thus, there remains a need for improved method for cleaning pipe systems, particularly oil tanker pipe systems, of residual amounts of hydrocarbons.